This invention relates generally to internal combustion engines, particularly engines for propelling motor vehicles. More specifically, the invention relates to an engine control system and method for improving stability of engine running speed when torque subtractions from gross torque change while the engine is running at a constant speed, such as at low idle speed.
Although a running engine in a motor vehicle develops a gross torque that is based essentially on engine fueling, the net torque that is available at the engine flywheel for delivery to the vehicle drivetrain is less than the gross torque. This is because of certain physical phenomena inherent in the engine as it is running and also certain loads that the engine drives other than the vehicle drivetrain. Consequently, net torque for the drivetrain is equal to gross torque minus total torque that is lost due to such phenomena and other engine loads.
With an engine running at a substantially constant speed such as low idle, a significant change in the total torque subtraction will occasion an incipient engine speed change, with engine speed becoming either higher or lower depending on whether the total torque subtraction increased or decreased. Although resulting disparity between actual engine speed and desired engine speed will be countered by closed-loop control seeking to correct the disparity, the quality of the correction may vary depending on various factors such as the magnitude of the total torque correction change and how fast it is changing. In other words, securing desired stability of engine speed may be difficult or even impossible to achieve in certain circumstances.
Consequently, it is believed that improvements for securing desired stability of engine speed in such circumstances would be beneficial.
The present invention relates to a system, strategy, and method that provide such improvements in an engine.
One generic aspect of the present invention relates to a method of operating an internal combustion engine that has a fueling system and that delivers net torque to a load. The method comprises: a) developing desired engine fueling data representing desired fueling for the engine; b) developing i) data representing a value of torque subtraction accounting for torque, that if added to net torque, would correspond to gross torque developed by the engine from fueling, ii) data representing speed at which the engine is running, and iii) data representing desired engine running speed. The torque subtraction data and the desired engine speed data are processed to develop feed-forward fueling data representing fueling that is projected to cause the engine to run at desired speed. The data representing speed at which the engine is running and the data representing desired engine running speed are processed to develop data representing engine speed error which is then processed according to one or more control functions each having gain determined by the torque subtraction data value to develop fueling adjustment data for compensating desired engine fueling for the torque subtraction data. The fueling adjustment data and the feed-forward fueling data are processed to develop desired engine fueling data representing desired fueling for the engine, with the engine fueling system fueling the engine in accordance with the desired engine fueling data.
Another generic aspect relates to an engine that operates according to the method just described.
Still other generic aspect relates to an engine control system for performing the method just described.